Instant Genius - From asteroids to aliens - how space is threatening our planet

Episode Date: September 25, 2025

Is our planet under threat from the depths of space? In this episode, we talk to solar physicist Dr Ryan French. Normally, Ryan is busy unravelling the mysteries of our Sun, but today we’ll be delving into a slightly darker topic – the many risks posed to our delicate planet from space. In his recent book, "Space Hazards: Asteroids, solar flares and cosmic threats”, Ryan covers all the many dangers our planet faces from space rocks, the Sun and the farthest reaches of the Universe. We run through some of the most pressing threats and find out just how worried we should be. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Hello and welcome to Instant Genius, a bite-sized masterclass in podcast form. Every Monday and Friday, you'll hear world-leading scientists and experts talking about the most fascinating ideas in science and technology today. I'm Ezzie Pearson, commissioning editor at BBC Science Focus. In today's episode, I'm talking to solar physicist Dr Ryan French, from the Laboratory for Atmospheric and Space Physics in Boulder, Colorado. Normally, Ryan is busy unraveling the mysteries of our Sun, but today we'll be delving into a slightly darker topic,

the many risks posed to our delicate Earth from space, be it asteroids, the Sun, or even from inside our own planet. Hello, Ryan, and welcome to Instant Genius. Hello, thanks for having me. So today we're going to be talking about all of the various ways that space is trying to kill us. A nice, happy and jolly topic. But it turns out there's actually quite a few ways that we might be wanting to take a look at the skies. So I think the hazard that most people are familiar with is probably asteroids.

There's been a bunch of Hollywood movies about it, episodes of TV shows. But how dangerous actually are these space rocks? Yes, that's an excellent question. So I think the most important thing to note is this isn't something we need to be worrying about right away, but it is a hazard that, as you say, is worth monitoring in the decades in the generations ahead. So most people have probably heard of meteors, right? A meteor or a shooting star, which you can see a shining streak across the night sky at certain points of the year, are essentially tiny, tiny fragments of much larger clouds of rock in space.

This could be from an asteroid, which is a rocky body that orbits the sun. This could be from a comet, which is sort of a gassy, dusty, icy body that orbits the sun as well. And fragments of these, when entering Earth's atmosphere, they burn up as meteors. But for a very small fraction of these meteors, they can make their way to the ground. And when that happens, we call the meteorites instead of meters. And meteorites, you know, there's a very large range of size here. Most of the ones you see in the night sky are no larger than a grain of sand and nothing to worry about. But when they start getting to the size of tens of meters wide or even hundreds of meters,

that's when we need to start worrying about these things. There seems to be a lot of things that can affect how dangerous an asteroid is. How do we gauge whether something's a threat or not? So there is a scale called the Torino scale, which attempts to answer that exact question. It considers two things. It considers the size of the object. So is it 10 meters across? Is it 100 meters across?

Is it a kilometer across? And that's when things start getting really scary. And what the impact would be if that were to hit Earth. And the second factor is what are the probability of this object striking Earth? If the probability is any larger than 1%, and the object is really any larger than, say, 10 meters, then it is something that is given a classification on this scale and something that we monitor very closely.

Are there any kinds of asteroids that are more dangerous than others? So really, seems like a silly answer to give, but the more dangerous ones are the ones with the higher probability of impacting Earth, right? So we care less about these giant asteroids that are sitting in the asteroid belt that are probably never ever going to come anywhere near Earth.

We care a lot less about them than the ones which are much smaller but do swing very close to Earth. There's a classification of asteroids called near-Earth objects, and there's a few different categories of these that intersect Earth's orbits at various distances in different ways, but these are certainly the ones to look out for. And you did mention there that comets are also a factor that could potentially be flying around. Are those a different type of risk to something like, say, an asteroid?

So really the risk is, again, whether it's a fragment of the comet or a fragment of the asteroid, the big factor is, one, the size. There is a second factor, which does, does play a role and that is the composition of the object, whether it is made of sort of ice, dust, how dense it is, if it's made of metal. So there is a slight difference there. Asteroids tend to be denser than their comet counterparts. But really, most of the meteorites that we get are just fragments of these objects and not the entire objects themselves. There has been some incidences where, we know this happens because asteroids have hit Earth in the past. The two that stand out to me are the ones that did for the dust.

dinosaurs a few million years ago, and the one that hit Chellibinsk, which was the town in Russia, back in 2013. And obviously, those are two very different size scales. How common are these different types of events from happening? Yeah, so the famous one, as you say, is sort of this global catastrophic dinosaur-sized extinction-level event. These are very, very rare. These happen. We're talking hundreds of millions of years apart. So 65 million years ago, or plus a little bit of change there. That was the last one of this scale. And this would truly, truly be catastrophic, right? But there are much smaller events which happen far more frequently, although don't pose as large of a risk as that one. So you mentioned the event in Russia in 2013. This was a smallish

object, about 15 meters across, entered the atmosphere. It actually burnt up fully before it made its way to the ground. So you might think, hey, great, fantastic. We got away without any damage, right? Unfortunately not. As it entered the atmosphere, it caused a large shockwave that propagated over hundreds of miles, really. And of course, this bright object entering the sky, everybody rushes to the window to look out the window and see what's happening. And this shock wave smashes glass in a very large radius. And there were over a hundred incidents of people going to the hospital because of glass smashing in their face. So not something that is ideal, but not a world-ending dinosaur-scale event. there is a spectrum of things to talk about here.

So the Chelyabinskwan, it exploded in the air, and some of them hit the ground, and also two-thirds of our planet is covered in water. What's the sort of relative risks between where exactly it comes down? So the biggest worry for sort of smaller-sized events are urban areas. So if these things happen and impact in the ocean, then perhaps this is not something we need to worry about too much. That happens in the middle of the tundra or the rainforest. Again, there's not too many people nearby. This reduces the risk. If an object entering the atmosphere is large enough, then they can actually trigger a tsunami like effects if they do impact the water. So this dinosaur event from 65 million years ago did exactly that,

produced a very large tsunami. But the objects have to be quite large to produce anything notable there. Now that we've thoroughly terrified all of our listeners, there's a famous saying that the dinosaurs went extinct because they don't have a space program. We now live a much more technologically advanced society. Can we do anything to prevent these kinds of events from happening? So the biggest thing that we can do is monitoring. So there are dedicated groups around the world that spend their time tracking objects of potential risk out there in space. They are given a ranking on this Torino scale that I mentioned earlier, and there are estimates made, or new observations are made to refine the probability and the likelihood of impacts happening. So there was an example

from earlier this year in February 2025, or January 2025, an asteroid was discovered, and it was initially given a decent-sized probability of impacting the Earth, about 2% or so. Following new observations, this probability rose to over 3% of an impact. This impact would have been in 2032. This is a little bit concerning. It was placed on this Torino scale. And then over the following weeks, more resources are dedicated to understanding this object. And as that happened, we became to learn, okay, great, the probability of this impacting Earth pretty much has fallen to 0% now. And we only know that because of the new resources that we put in to learning about this object. If something were confirmed to be heading our way, there are some rudimental

estimates that can be made about where this might burn. up or enter the atmosphere where and when, so you can begin to make some plans there and think about, oh, is this an urban area that we need to think about evacuating? If it's anything larger, then we're entering the realm of possibility but not quite feasibility. There was a NASA mission over the last few years called Dart, which is the double asteroid redirection test. Now, Dart proved our ability to redirect very slightly the orbit of of an asteroid. And the way it does this, it's not very scientific.

It basically, this satellite just smashes into the asteroid as hard as it can in order to try and move its direction slightly and change its orbit. And it was verified that for this small asteroid, its orbit had been changed. Now, this was a very small asteroid in an orbit that was not heading towards Earth, but it is the first test in what might one day

become a program that can redirect Earth-directed asteroids. And how big is the scale of this sort of tracking program? How many asteroids do we actually know about? There are a few tens of thousands, over 30,000 now, near-ear-earth objects that are being tracked. So these aren't the asteroids that are out in the asteroid belts. These are asteroids that have an orbit passing close enough to us to warrant closer observation. So meteors are probably the most famous space danger that people know about, not familiar with. But one of the threats that they're probably being not as familiar with is

something that we're actually usually happy to see, which is the sun. So what hazards does our sun pose to Earth? That's a brilliant question. And this is my area of research. So I'm a solar astrophysicist, so I spend a lot of time researching the sun, something I love talking about, writing about. The sun, very different to the asteroid's threat in that the worst-case scenario is, not as bad. We're not talking extinction level events possible from the sun like they would be from asteroids, but the effects are far more immediate and far more common. So the atmosphere of the sun is constantly changing. When we see the sun in the sky on a sunny day, as you say, we're always happy to see. We see it as a bright orb of light and it doesn't seem to be doing very much. But if you

have the right equipment, the right filter, even solar telescopes you can buy from the ground, you can quickly tell the sun is changing all the time. Day to day, even hour to hour, the sun is doing stuff. Now, the atmosphere of the sun is actually dominated by magnetic fields. We probably all know about magnets, stick your fridge magnet to your fridge. The earth has a magnetic field, which a compass will point to, right? That's how a compass points north. The sun also has a very strong magnetic field.

But unlike the Earth, which has a very simple magnetic field, the sun's magnetism is very complicated. It's always twisting, turning, things are getting tangled together. And as this happens, we get bursts of energy from the sun, where this magnetic field is converted into light and the acceleration of small particles. And this is called a solar flare. So many people probably have heard the term solar flare, but don't know exactly what it means. And a solar flare is just a conversion of energy in the atmosphere of the sun.

And a solar flare can produce something else, which sounds like a very complicated word, something called a coronal mass ejection or a CME for short. This sounds complex, but if you break it down, a coronal mass ejection is an ejection or an eruption from the sun. It's an eruption of mass of stuff, right, from the sun's atmosphere, which we call the corona. So that's where the term coronal mass ejection comes from. And this takes a few days to reach Earth between maybe one to four days depending on the speed that this stuff is traveling. It can travel around 2,000 kilometers every second, which is a couple of million miles per hour. So really, really rapid stuff. And when this reaches Earth and when it impacts our planet and our magnetic field,

it can cause a few strange things to happen. First and foremost, a very fun aspect of this, and this is the only fun aspect of this is when these particles from this eruption slam into Earth's magnetic field, they can sort of enter our magnetic field, flow down, and they hit our upper atmosphere. And as our upper atmosphere gets collided from these particles from the sun, it causes them to glow. And that is what we see as the northern lights. So this is a fun side effect of activity of the sun is the aurora. The downside is not only can it cause the aurora, but it can begin to disrupt technological systems as well. So satellites, satellite communications, satellite navigation, power grids, even railroad networks, things like that,

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Visit focal powered by name.com for more information. So we've got these massive flares that are coming in from the sun. we can monitor them from Earth, but how much warning do we get when we know one's incoming? So it's important when answering this to distinguish the difference between the solar flare and the coronal mass ejection. So solar flares come from sort of complex regions on the sun,

which we call sunspots, and we can look at a sunspot on the sun, and we're not yet at the stage where we can say, okay, this region on the sun is about to cause a solar flare. But we can say this region on the sun kind of has a 20% chance of producing a flare. Last time we saw something like this, maybe it produced a flare one in five times. So at that point, that's still an area of ongoing research. But when the flare happens, the flare is light that travels at the speed of light.

We see that instantly. We see the flare and we can see following the flare whether or not there is an eruption or a CME associated with that flare. and from that we can then forecast how long it is going to take to reach Earth, if it is going to reach Earth, and what the impacts might be if it does. And that lead time is between sort of a day to four-ish days. And are there any times when we need to be particularly keeping an eye on the sun? It kind of depends what you do and who you are. So if you are an everyday person and you have a job that does not involve things in space,

then probably you don't need to care about the sun very often. If you are someone who works in satellite operations, for example, though, you care about the sun all the time, really. When small flares happen, small flares that, you know, normal people wouldn't notice or that wouldn't make the news. Even small flares can require corrections to the orbit of your satellites and things like that. There was an example from 2022 where SpaceX launched a... series of satellites into space. They launched 60 Starlink satellites during a solar flare and only

20 of the 60 made it to space. 40 of them de-orbited and burnt up in the atmosphere. There was an example last year in May 2024, a very famous event. We had an extreme solar storm or a geomagnetic storm is the official scientific term. This was caused by a series of these eruptions hitting Earth in relatively short succession. The Northern Lights were viewed pretty much all over Europe and a normal. America and in the southern hemisphere as well. It was a fantastic event. But there were damages to industry as a result of this. In the United States, the agricultural industry, which relies on satellite navigation, automated tractors, there's no people sitting in these things, they just use GPS, didn't work for a full weekend because of this event and there was a half a billion

dollar loss in the industry. In the United Kingdom, there were overheating alarms triggered at various points in the power grid, but thankfully nothing to the point of failure. So again, if you work in farming or you work in power companies, you care about these things. And there is a cycle of activity on the sun, which I think you may have been alluded to in your question there. There is a cycle on the sun which lasts about 11 years. So we call this the solar cycle. At the bottom of this cycle, these events are pretty rare, but they can still happen. So if you work in a very specific industry. You do care about the sun at this solar minimum period, as it's called. But at solar maximum, at the peak of this 11 year cycle, these things are far more common. So indeed, industry,

even people who want to see the aurora should be paying attention to what the sun is doing during these times. And our best guest currently is probably we reached the peak of this solar cycle last year in October 2024. It sounds like it causes a lot of problems for people up in and it's sometimes managed to make it down to Earth. Has there ever been any incidences where there's been a big problem or a big occurrence here on Earth? There are a few examples, yes. So some recent examples back in 2003, an extreme geomagnetic storm caused power outages in

Sweden and South Africa. Back in 1989, there was another example where the east coast of Canada, a hydroelectric plant failed. and over a million people were without electricity for 13 hours or so. Moving back was in time. There were even further examples. Back in 1912, there was a fire that broke out in a New York Railroad station as a result of this activity from the sun.

And what we often consider to be the sort of quote unquote, worst case scenario hasn't happened since 1859. It was a very famous solar flare. It was called the Carrington event. if people want to look it up more at home. And during this counter event in North America, the Northern Lights were seen everywhere, probably the brightest display of Aurora ever seen on human record.

And over in Europe, it was daytime, so we didn't get the same display of the Aurora. But telegraph machines, which were the peak of technology at the time, started sending and receiving random messages, not sort of full sentences, but random letters, numbers, symbols, started coming through on the telegraph machine. And as operators went to try and fix this,

they would get electric shocks. There'd be sparks. Really strange things would start happening. And this was the first time that it has sort of been demonstrated by an astronomer called Richard Counton. That the sun, an activity on the sun, can cause this strange stuff happening here at Earth. So it's good that we've now been monitoring that sort of thing,

because if that happened today, it would be a bit of a bigger issue. Yeah, obviously today are. Our reliance on technology falls a bit beyond telegraph machines. A little bit, a little bit. A little bit. So there are various estimates as to what would happen if that event happened today. Sort of a moderate estimate would be you might have some regional power outages, maybe lasting a couple of days.

Maybe as many as one in five satellites might stop working. there may be sort of grounded flights for several days while the radiation is high in the atmosphere, satellite navigation and communication as well, so this farming example I said earlier would last a few days as well. So we're not talking apocalyptic world-ending stuff, which I think is very important to note. Sometimes when you see people talk about solar flares, there is this apocalyptic hat on, and that's not the reality of the situation. But the reality of the situation is in a worst-case scenario, which we might expect every 200 years or so, there would be significant economic disruption,

travel disruptions, financial disruptions, and sort of the financial impact of that could be in tune with the largest other natural disasters, except with no direct threat to human life. The cause of these problems comes from the sun's reaction with Earth's magnetic field, and that field is generated inside the core of our own planet. And you talked about in your book that actually there's some things going on there that we might need to pay attention.

So can you tell us what's going on with our planet's magnetic field? So Earth has a magnetic field. This magnetic field is generated by our core. So we have an iron solid core in the middle of Earth and there's a liquid outer core around that as well. And as the Earth rotates, it generates a magnetic field around Earth. This magnetic field is not constant, though. This evolves and changes with time. There are a few different things that can happen.

Every few hundred thousand years, this magnetic field flips completely. The North Pole becomes the South Pole, the South Pole becomes the North Pole. And also in time, it can very faintly weaken a little bit, strengthen a little bit as well. And it's important to understand our magnetic field because the magnetic field does protect us from the sun and other cosmic radiation. The magnetic field naturally drifts, as I say. There is currently no firm evidence to suggest that the natural drifting of the field that we're currently seeing is going to lead to any large problems like the magnetic field flipping or weakening like that. It is also true and it's often shared in online circles that the magnetic field has weakened somewhat in the last century.

And this is true. The magnetic field is about 10% weaker now than it was 100 years ago. But it's about average compared to this last 100,000 years. We can tell this from geological records. So at the moment, a magnetic field is nothing to be concerned about. It is acting as a shield, protecting us from the sun and the cosmic rays and everything beyond that as well. But over the time scales of tens of thousands or hundreds of thousands of years, there are processes that could expose us a little bit more to these things in space.

But at the moment, it doesn't seem to be we're heading in that direction anytime soon. So that's great to hear that Earth's magnetic field isn't going anywhere anytime soon. But are there any other examples where it did go away? Yes, absolutely. So one of our nearest neighbours in the solar system, the planet Mars, the red planet, nowadays is a barren red wasteland. It is a dusty environment. It gets its red colour from iron oxide, which is just rust.

You've had a rusty bicycle or a rusty nail. That's what gives Mars its red colour. But Mars didn't used to be like this. Mars used to be a rich, wet environment quite similar to Earth. We know this because when you look at Mars, there is geological evidence of rivers, of canyons, of lakes and seas, things that we see here on Earth. And you can look up satellite imagery and you can make a direct comparison between the Grand Canyon and a canyon on Mars, for example, right?

And so all evidence points to the fact that Mars used to have this rich atmosphere and this rich water on its surface. So the question is what happened between then and now? Well, the answer we think comes down to Mars's magnetic field, as you were suggesting. Magnetic fields, as I said before, they can protect us from the sun and cosmic rays and things like that. And one role that they play in doing this is by protecting gases in the atmosphere. Without a magnetic field, we are exposed directly to particles from the sun that very slowly over time can strip away gases from the atmosphere. of Mars or wherever you're talking about, right? Mercury doesn't have an atmosphere for this exact reason as well. And so over time, Mars, which once had a magnetic field, it lost most of its magnetic

field. It's got a tiny, tiny bit left, but its magnetic field disappeared, and then its atmosphere was lost, and all the water evaporates into space. And just like that, over the period of a few million years, Mars went from an Earth-like planet to a planet with no permanent water on its surface. And by water, I mean liquid water, because there is permanent water ice on Mars still. Everything we've talked about so far has been very close to home within our own solar system. But there are some threats that are coming from a little bit further afield. So my personal favourite constellation is Orion. And in Orion, there's a star called Beetle Juice, which is a red giant on the way to going supernova and exploding. Do we have anything to worry about when that

happens. Thankfully, beta juice is a little bit beyond the zone of immediate danger. So, beta juice, as you say, is a red supergiant. It is approaching the end of its life. And when a star that large reaches the end of its life, it goes supernova, is the term. This is a very large explosion, essentially, or rather an implosion followed by an explosion where a star collapses in on itself to form a neutron star or a black hole. This won't happen with the sun, but does happen with much larger stars. Now, Beetlejuice, relatively speaking, will go supernova soon. But by soon, we could mean tomorrow or we could mean 100,000 years from now. So that's soon, cosmically speaking. When this happens, when Beetle Juice does go supernova, it will be visible in the daytime sky.

It will be bright enough as a star, that it will be brighter than the moon. And in the blue sky, in the middle of the day, you will be able to see it. This has happened in the past. About 1,000 years ago, there was a supernova explosion recorded by ancient Chinese astronomers. It lasted in the sky for a couple of weeks. And when we point telescopes to the part of the sky described by these astronomers,

we are greeted by the Crab Nebula, which is a remnant of this supernova that occurred 1,000 years ago. If Beatrice were to happen, I would have to go supernova now, we would receive a rise in cosmic rays, and these are high-energy particles coming from outer space. Thankfully, it's too far away to do any real damage to our atmosphere or life on Earth. If any nearby stars were to go supernova, this would be a big problem for us,

but thankfully this is not something we have to worry about for tens of millions of years. And possibly venturing a little bit more into the speculative. rather than the scientific here. One of the big threats from space that people always worry about is aliens. So how much do you think we actually need to worry about an alien invasion? That is a fantastic question

and one I get asked all the time as an astrophysicist, and I'm always, always happy to answer. So there are two questions there, I think. The first one is, are there aliens? Do I believe in aliens? And that question can mean a lot of things, right? Do I believe there is life out there?

Yes, 100%. Do I believe there is intelligent life out there? This kind of life that may be are hosting a podcast about Earth and the sun from the other side of the galaxy. Possibly. But that life, if it is there, is far enough away that we will likely never know about them and they will likely never know about us either. So really when we talk about life as an immediate threat, we're really not talking about intelligent life, we're not talking sci-fi, UFOs, invasions, things like that. But there are extraterrestrial risks that we do need to think about a bit closer to home.

So there are places in the solar system where there are candidates, locations that are candidates for very basic primitive life. Some of the moons of Jupiter, the moons of Saturn, are possible candidates here. we have Europa and Ganymede around Jupiter, Enceladus, even Titan, which are moons around Saturn. Even Mars, there's a possibility that there could be very basic, microbial type life. There was some recent evidence that came out just last week, which suggests there could be some evidence for fossils of extinct life on Mars. I won't go into that too much. I should also add, that was last week when we were recording it. When this goes out, it was probably a bit more in the past.

Yes, that was probably a bit more in the past last week from this conversation. And so, you know, it's possible that in the solar system there is this very basic primitive life. Would that pose a risk to us? We don't really know. We don't know what our immune systems, how they might respond to microbial life from other objects. And similarly, we don't know how they might respond to us. So this risk, probably in the immediate time frame, goes the other direction. When we visit Mars and we have spacecraft currently visiting some of the moons of Jupiter and eventually Saturn,

we need to be careful that we don't contaminate these environments and pose a risk to any life that potentially may be there. So in the long run, you know, we're not expecting any samples to be returned from the moons of Jupiter to Earth any time soon, but we are sending probes out there. So we do need to be careful with cross-contamination. Well, thank you very much for taking your time to talk to us today. day, Ryan. Hopefully, our listeners have come to realize that whilst there are some risks out there from the deep dark void of space, we're probably going to be okay. They're not that much to worry about. But thank you very much for chatting to us. Yes, thank you for having me and

absolutely want to finish on an optimistic tone there that these threats in space, the sun, asteroids, these other objects, these are things that as years past, as decades past, we are becoming more immune and better prepared for any potential hazards out there. Thank you for listening to this episode of Instant Genius, brought to you by the team behind BBC Science Focus. That was Dr Ryan French. To discover more about the topics we've discussed, check out their latest book, Space Hazards, Asteroids, Solar Affairs and Cosmic Threats. If you liked what you just heard, please consider subscribing to Instant Genius on your preferred podcast platform. If you'd like to see our guests and hosts in person, why not check out our YouTube channel at ScienceFocus.

The current issue of BBC Science Focus is out now. Pick up a copy wherever you buy your favourite magazine or download us on your app store of choice. You can also find us on Apple News or online at sciencefocus.com. This podcast is sponsored by Name, Audio and Focal. The texture and emotional depth of music can be lost through digital sources or poor signal. Name Audio believes you can have digital precision with analog warmth. Alongside French acoustic specialist vocal, Name creates high-end audio systems combining innovation with craftsmanship,

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